Design of Flexible Films Based on Kinked Carbon Nanofibers for High Rate and Stable Potassium-Ion Storage

With the emergence of wearable electronics,flexible energy storage materials have been extensively studied in recent years.However,most studies focus on improving the electrochemical properties,ignoring the flexible mechanism and structure design for flexible electrode materials with high rate capacities and long-time stability.In this study,porous,kinked,and entangled network structures are designed for highly flexible fiber films.Based on theoretical analysis and finite element simulation,the bending degree of the porous structure(30%porosity)increased by 192%at the micro-level.An appropriate increase in kinking degree at the meso-level and contact points in entanglement network at the macro-level are beneficial for the flexibility of fiber films.Therefore,a porous and entangled network of sulfur-/nitrogen-co-doped kinked carbon nanofibers(S/N-KCNFs)is synthesized.The nanofiber films synthesized from melamine as nitrogen sources and segmented vulcanization exhibited a porous,kinked,and entangled network structure,and the stretching degree increased several times.The flexible S/N-KCNFs anode delivered a higher rate performance of 270 mAh g−1 at a current density of 2000 mA g−1 and a higher capacity retention rate of 93.3%after 2000 cycles.Moreover,the foldable pouch cell assembled by potassium-ion hybrid supercapacitor operated safely at large-angle bending and showed long-time stability of 88%capacity retention after 4000 cycles.This study provides a new idea and strategy for the flexible structure design of high-performance potassium-ion storage materials.

Enabling Multi-Chemisorption Sites on Carbon Nanofibers Cathodes by an In-situ Exfoliation Strategy for High-Performance Zn–Ion Hybrid Capacitors

Carbon nanofibers films are typical flexible electrode in the field of energy storage,but their application in Zinc-ion hybrid capacitors(ZIHCs)is limited by the low energy density due to the lack of active adsorption sites.In this work,an in-situ exfoliation strategy is reported to modulate the chemisorption sites of carbon nanofibers by high pyridine/pyrrole nitrogen doping and carbonyl functionalization.The experimental results and theoretical calculations indicate that the highly electronegative pyridine/pyrrole nitrogen dopants can not only greatly reduce the binding energy between carbonyl group and Z n2+by inducing charge delocalization of the carbonyl group,but also promote the adsorption of Zn2+by bonding with the carbonyl group to form N–Zn–O bond.Benefit from the multiple highly active chemisorption sites generated by the synergy between carbonyl groups and pyridine/pyrrole nitrogen atoms,the resulting carbon nanofibers film cathode displays a high energy density,an ultralong-term lifespan,and excellent capacity reservation under commercial mass loading(14.45 mg cm-2).Particularly,the cathodes can also operate stably in flexible or quasi-solid devices,indicating its application potential in flexible electronic products.This work established a universal method to solve the bottleneck problem of insufficient active adsorption sites of carbon-based ZIHCs.Imoproved should be changed into Improved.

Precisely controlling the twist angle of epitaxial MoS_(2)/graphene heterostructure by AFM tip manipulation

Two-dimensional(2D)moirématerials have attracted a lot of attention and opened a new research frontier of twistronics due to their novel physical properties.Although great progress has been achieved,the inability to precisely and reproducibly manipulate the twist angle hinders the further development of twistronics.Here,we demonstrated an atomic force microscope(AFM)tip manipulation method to control the interlayer twist angle of epitaxial MoS_(2)/graphene heterostructure with an ultra-high accuracy better than 0.1°.Furthermore,conductive AFM and spectroscopic characterizations were conducted to show the effects of the twist angle on moirépattern wavelength,phonons and excitons.Our work provides a technique to precisely control the twist angle of 2D moirématerials,enabling the possibility to establish the phase diagrams of moiréphysics with twist angle.

Enhanced potassium storage of carbon nanofibers as binderfree anodes enabled by coupling ultra-small amorphous Sb_(2)O_(3),graphene modification and sulfur doping

Considering the intrinsic advantages of natural copiousness and cost-effectiveness of potassium resource,potassium-ion batteries(KIBs) are booming as prospective alternatives to lithium-ion batteries(LIBs) in large-scale energy storage scenarios. Nevertheless, lacking desirable electrodes for reversibly hosting the bulky K+hinders the widespread application of KIBs, and it needs to be urgently solved. Hereon, the porous S-doped Sb_(2)O_(3)-graphene-carbon(SAGC) nanofibers are manufactured through an adjustable and facile approach, which involves electrospinning, in situ etching and sulfuration. The synthesized SAGC is featured by the ultra-small amorphous Sb_(2)O_(3) homogeneously wrapped inside the carbon matrix, as well as the co-incorporation of graphene and sulfur. Tentatively,the SAGC nanofiber sheets are applied as binder-free anodes for KIBs, exhibiting a prominent cycling life(256.72 m Ah·g^(-1) over 150 cycles at 100 m A·g^(-1)) and rate·g^(-1) over 100 cycles at 1 A·g^(-1)). The positive synergy among all the active components accounts for the distinguished performances of the SAGC. By reinforcing the tolerability to the swelling stress, producing the valid electrochemical active sites, and promoting the charge transferring for reversible K+uptake, the SAGC finally renders the excellent cyclability, capacity, and rate capability. Moreover, the extrinsic electrochemical pseudocapacitance characteristics induced by the porous carbon substrate elevate the K-storage capacity of the SAGC as well. It is hoped that the conclusions drawn may offer new insights into a direction for the high-performance binderfree KIB anodes.

Low palladium content CeO_(2)/ZnO composite for acetone sensor with sub-second response prepared by ultrasonic method

In practical applications,noble metal doping is often used to prepare high performance gas sensors,but more noble metal doping will lead to higher preparation costs.In this study,CeO_(2)/ZnO-Pd with low palladium content was prepared by ultrasonic method with fast response and high selectivity for acetone sensing.With the same amount of palladium added,the selectivity coefficient of CeO_(2)/ZnO-Pd is 1.88 times higher than that of the stirred sensor.Compared with the pure PdO-doped CeO_(2)/ZnO-PdO material,the content of Pd in CeO_(2)/ZnO-PdO is about 30%of that in CeO_(2)/ZnO-PdO,but the selectivity coefficient for acetone is 2.56 times higher.The CeO_(2)/ZnO-Pd sensor has a higher response(22.54)to 50×10^(−6) acetone at 300℃and the selectivity coefficient is 2.57 times that of the CeO_(2)/ZnO sensor.The sensor has a sub-second response time(0.6 s)and still has a 2.36 response to 330×10^(−9) of acetone.Ultrasonic doping makes Pd particles smaller and increases the contact area with gas.Meanwhile,the composition of n-p-n heterojunction and the synergistic effect of Pd/PdO improve the sensor performance.It shows that ultrasonic Pd doping provides a way to improve the utilization rate of doped metals and prepare highly selective gas sensors.

Heterointerface Engineering-Induced Oxygen Defects for the Manganese Dissolution Inhibition in Aqueous Zinc Ion Batteries

Manganese-based material is a prospective cathode material for aqueous zinc ion batteries(ZIBs)by virtue of its high theoretical capacity,high operating voltage,and low price.However,the manganese dissolution during the electrochemical reaction causes its electrochemical cycling stability to be undesirable.In this work,heterointerface engineering-induced oxygen defects are introduced into heterostructure MnO_(2)(δa-MnO_(2))by in situ electrochemical activation to inhibit manganese dissolution for aqueous zinc ion batteries.Meanwhile,the heterointerface between the disordered amorphous and the crystalline MnO_(2)ofδa-MnO_(2)is decisive for the formation of oxygen defects.And the experimental results indicate that the manganese dissolution ofδa-MnO_(2)is considerably inhibited during the charge/discharge cycle.Theoretical analysis indicates that the oxygen defect regulates the electronic and band structure and the Mn-O bonding state of the electrode material,thereby promoting electron transport kinetics as well as inhibiting Mn dissolution.Consequently,the capacity ofδa-MnO_(2)does not degrade after 100 cycles at a current density of 0.5 Ag^(-1)and also 91%capacity retention after 500cycles at 1 Ag^(-1).This study provides a promising insight into the development of high-performance manganese-based cathode materials through a facile and low-cost strategy.

Electrospinning with sulfur powder to prepare CNF@G-Fe_(9)S_(10) nanofibers with controllable particles distribution for stable potassium-ion storage

As anode materials of electrochemical energy storage system,metal sulfides with high theoretical capacities suffer from issues of materials smashing and deactivation due to huge volume change,resulting in the inferior cycle stability.In this paper,a new strategy of adding sulfur powder into the electrospinning precursor instead of employing sulfur powder during the sulfurizing treatment is proposed to prepare Fe_(9)S_(10)composites(CNF@G-Fe_(9)S_(10)-1).In those composites,most of Fe_(9)S_(10)particles are embedded in the graphene-carbon fibers with multiple protection.As anodes for potassium-ion batteries,CNF@G-Fe_(9)S_(10)-1 display higher rate capacities and more excellent stability(103.2 mAh·g^(-1)at 1000 mA·g^(-1)after 892 cycles)than Fe_(9)S_(10)composites synthesized by the traditional method.In addition,as anodes for potassiumion hybrid capacitors,they also deliver high capacities of102.8 mAh·g^(-1)at 1000 mA·g^(-1)after 100 cycles.The morphology characterization evidences indicate that the surface and integrity of CNF@G-Fe_(9)S_(10)-1 are more smooth and complete than the Fe_(9)S_(10)composites fabricated using a common method without sulfur power in electrospinning precursor.The excellent stability and high capacity of CNF@G-Fe_(9)S_(10)-1 can be attributed to nearly full-wrapped structure of Fe_(9)S_(10)in the carbon matrix arising from the new strategy.Owing to the formation of the structure,Fe_(9)S_(10)particles are protected from the pulverization,and the structure stability of hybrid carbon fibers is enhanced.This study may provide a new strategy for the controllable synthesis of metal sulfide-CNFs and their application for high stability energy storage.

Promoting the optoelectronic and ferromagnetic properties of Cr_(2)S_(3)nanosheets via Se doping

Doping can change the band structure of semiconductors,thereby affecting their electrical,optical,and magnetic properties.In this study,we describe the synthesis of two-dimensional(2D)Se-doped Cr_(2)S_(3)(Se-Cr_(2)S_(3))nanosheets using the chemical vapor deposition method.In these semiconductor nanosheets,the Se doping concentration can be controlled by tuning the Se/S mass ratio in the precursor.At the doping concentrations of 10.05%and 2.05%,the room temperature conductivity and mobility were increased by nearly 4 and 2 orders of magnitude,respectively.In addition,the response time of an ultrathin Se-Cr_(2)S_(3)photodetector was 200 times shorter than that of an undoped Cr_(2)S_(3)nanosheet photodetector.4.07%-Se-Cr_(2)S_(3)nanosheets show ferrimagnetic behavior with a Curie temperature of~200 K,which is 80 K higher than that of undoped Cr_(2)S_(3)nanosheets.A density functional theory calculation indicated that the Se doping can induce the formation of intercalated Cr vacancies in SeCr_(2)S_(3)and enhance its metallic characteristics.Our results demonstrated that Se-Cr_(2)S_(3)has significant potential in future electronic,optoelectronic,and spintronic devices.

Pyridine-regulated Sb@InSbS_(3)ultrafine nanoplates as high-capacity and long-cycle anodes for sodium-ion batteries

Sb-based materials exhibit considerable potential for sodium-ion storage owing to their high theoretica capacities.However,the bulk properties of Sb-based materials always result in poor cycling and rate performances.To overcome these issues,pyridine-regulated Sb@InSbS_(3)ultrafine nanoplates loaded on reduced graphene oxides(Sb@InSbS_(3)@rGO)were designed and synthesized.During the synthesis process,pyridine was initially adopted to coordinate with In^(3+),and uniformly dispersed In_(2)S_(3)ultrafine nanoplates on reduced graphene oxide were generated after sulfidation.Next,partial In^(3+)was exchanged with Sb^(3+),and Sb@InSbS_(3)@rGO was obtained by using the subsequent annealing method.The unique structure of Sb@InSbS_(3)@rGO effectively shortened the transfer path of sodium ions and electrons and provided a high pseudocapacitance.As the anode in sodium-ion batteries,the Sb@InSbS_(3)@rGO electrode demonstrated a significantly higher reversible capacity better stability(445 m Ah·g^(-1)at 0.1 A·g^(-1)after 200 cycles and 212 mAh·g^(-1)at 2 A·g^(-1)after 1200 cycles),and superior rate(210 mAh·g^(-1)at 6.4 A·g^(-1))than the electrode without pyridine(355 mAh·g-1at 0.1 A·g-1after 55 cycles and 109 mAh·g^(-1)at 2 A·g^(-1)after 770 cycles)Furthermore,full cells were assembled by using the Sb@InSbS_(3)@rGO as anode and Na_(3)V_(2)(PO_(4))_(3)as cathode which demonstrated good cycling and rate performances and exhibited promising application prospects.These results indicate that adjusting the microstructure of electrode materials through coordination balance is A·good strategy for obtaining high-capacity,high-rate,and longcycle sodium storage performances.

人工道德基础器件:模拟道德逻辑的晶体管

日益先进的人工智能在生活中的广泛应用,促进了人工道德问题的产生.机器人的人工伦理的建立和实施通常是通过被动程序指令解决的,而在硬件层面的主动实现仍然具有挑战性.在这里,受认知心理学和神经生理学的启发,我们展示了一种典型的人工道德器件.通过判断善恶和解决道德困境,器件实现了机器人三定律中的第一定律.器件展示了自我、本我和超我三种状态,以及绝对命令、本能漠视、本能冲动、道德义务论、功利主义和利己主义等六种人性.道德的起源在电子学方面得到了揭示,这是潜意识和意识之间的对抗性协作.这项工作为未来人工智能的意识产生和道德形成提供了一条可行的道路.

具有异质结构的多功能氧化石墨烯改性纳米纤维膜(ZnS-CoS@GO@CNFs)用于长期稳定的钾离子储存

过渡金属硫化物作为钾离子电池的高理论容量阳极,由于其电导率低、循环过程体积膨胀大,导致其倍率性能和循环稳定性较差.本文采用氧化石墨烯(GO)来控制纳米颗粒在纤维中的粒径和分布,以提高复合纤维的导电性和拉伸变形.此外,由异质结构和氧化石墨烯组成的三维导电碳网络(ZnS-CoS@GO@CNFs)可以加速钾离子储存的动力学并稳定钾离子储存.作为钾离子电池的阳极材料,该复合材料在3 A g^(−1)下具有210 mA h g^(−1)的优异倍率性能.在2 A g^(−1)的大电流下经历2800次循环后仍表现出171 mA h g^(−1)的容量,容量保持率为97.7%.此外,当纳米纤维膜用作自支撑阳极时,仍然可以保持稳定的容量输出(在0.1 A g^(−1)下100次循环后容量为302 mA h g^(−1)).由钾离子混合电容器组装的可折叠袋状电池在多角度重复弯曲和最终恢复的情况下仍然可以安全地工作,并且可以提供大的能量密度(134 W h kg^(−1))和功率密度(5815 W kg^(−1)).优异的电化学性能进一步揭示了多功能氧化石墨烯复合纤维膜的应用前景.

铁电突触器件及其应用的研究进展

类脑计算是后摩尔时代集成电路发展的重要方向,开发能够模拟理想突触行为的人工突触器件是构建神经元-突触-神经元连接方式的类脑计算芯片的关键.铁电薄膜材料具有独特的非易失性极化,极化的可塑性与生物突触的可塑性十分类似,因此铁电突触器件近年来受到了广泛关注.本文从器件突触功能模拟和类脑计算应用两个方面对铁电突触器件的研究进展进行了综述.结果表明,铁电突触器件具有两端和三端两种典型结构.除了能有效模拟生物突触功能,铁电突触器件还具有结构简单、功耗低、稳定性高、开关比大及编程速度快等优点.在应用层面,基于铁电突触的神经网络在图像识别方面的研究取得了一系列进展.此外铁电突触还被应用于触觉和视觉仿生.虽然取得了丰富的研究进展,但铁电突触器件目前仍停留在原理的提出和实验验证阶段,在突触性能调控机理、可靠性评价标准、阵列结构优化设计、高密度集成工艺、神经形态计算架构设计、新颖应用场景拓展等方面的研究都存在不小的挑战,这些也是未来铁电突触研究所要聚焦的方向.

Review on metal halide perovskite-based optoelectronic synapses

With the progress of both photonics and electronics,optoelectronic synapses are considered potential candidates to challenge the von Neumann bottleneck and the field of visual bionics in the era of big data.They are also regarded as the basis for integrated artificial neural networks(ANNs)owing to their flexible optoelectronic tunable properties such as high bandwidth,low power consumption,and high-density integration.Over the recent years,following the emergence of metal halide perovskite(MHP)materials possessing fascinating optoelectronic properties,novel MHP-based optoelectronic synaptic devices have been exploited for numerous applications ranging from artificial vision systems(AVSs)to neuromorphic computing.Herein,we briefly review the application prospects and current status of MHP-based optoelectronic synapses,discuss the basic synaptic behaviors capable of being implemented,and assess their feasibility to mimic biological synapses.Then,we focus on the two-terminal optoelectronic synaptic memristors and three-terminal transistor synaptic phototransistors(SPTs),the two essential apparatus structures for optoelectronic synapses,expounding their basic features and operating mechanisms.Finally,we summarize the recent applications of optoelectronic synapses in neuromorphic systems,including neuromorphic computing,high-order learning behaviors,and neuromorphic vision systems,outlining their potential opportunities and future development directions as neuromorphic devices in the field of artificial intelligence(AI).

Perovskite/GaAs-nanowire hybrid structure photodetectors with ultrafast multiband response enhancement by band engineering

We developed a hybrid structure photodetector combining one-dimensional(1D)inorganic GaAs nanowires and two-dimensional(2D)organic perovskite materials,which can achieve various performance enhancements using a relatively simple structure.Via the optical absorption enhancement of perovskite and the type-II energy band structure formed by the heterostructure,the responsivity and detectivity of the photodetector from ultraviolet(UV)to visible(Vis)wavelengths are significantly enhanced,reaching 75 A/W and 1.49×10^(11)Jones,respectively.The response time of the photodetector was significantly decreased by 3 orders,from 785 ms to 0.5 ms,and the dark current was further reduced to 237 fA.A photodetector was prepared with enhanced responsivity and ultrafast response time in the multiband region from the UV to Vis wavelength.To the best of our knowledge,this is the first time to combine inorganicⅢ-ⅤGaAs nanomaterials with organic perovskite materials,which verifies the effective combination of inorganic and organic materials in a mixed dimension.The excellent photoelectric performance of the perovskite/GaAs-nanowire hybrid structure photodetector makes it a potential candidate material for a wide range of photoelectric applications such as multiband photodetection.

Multimodal MEMS vibration energy harvester with cascaded flexible and silicon beams for ultralow frequency response

Scavenged energy from ambient vibrations has become a promising energy supply for autonomous microsystems.However,restricted by device size,most MEMS vibration energy harvesters have much higher resonant frequencies than environmental vibrations,which reduces scavenged power and limits practical applicability.Herein,we propose a MEMS multimodal vibration energy harvester with specifically cascaded flexible PDMS and"zigzag"silicon beams to simultaneously lower the resonant frequency to the ultralow-frequency level and broaden the bandwidth.A two-stage architecture is designed,in which the primary subsystem consists of suspended PDMS beams characterized by a low Young's modulus,and the secondary system consists of zigzag silicon beams.We also propose a PDMS lift-off process to fabricate the suspended flexible beams and the compatible microfabrication method shows high yield and good repeatability.The fabricated MEMS energy harvester can operate at ultralow resonant frequencies of 3 and 23 Hz,with an NPD index of 1.73μW/cm^(3)/g^(2)@3 Hz.The factors underlying output power degradation in the low-frequency range and potential enhancement strategies are discussed.This work offers new insights into achieving MEMS-scale energy harvesting with ultralow frequency response.

Sulfonate-functionalization in Zn-iodine batteries as one stone kills two birds:iodine limiter and uniform Zn plating guidance layer

Aqueous Zn-iodine(Zn-I_(2))batteries have attracted extensive research interest as an emerging redox conversion energy storage system due to the low cost and high safety.However,the shuttling effects of polyiodides arising from incomplete redox conversion and inhomogeneous Zn plating on the Zn anode surface always hinder the commercial application of Zn-I_(2)batteries.In this work,a two-birds-with-one-stone strategy is reported for long-life Zn-I_(2)batteries.Based on the strategy,the sulfonate-functionalized carbon fiber not only acts as the excellent iodine limiter to inhibit iodine species shuttling,but also as the uniform Zn plating guidance layer on the Zn anode surface to prevent the inhomogeneous deposition of Zn^(2+).Consequently,a superior cycling stability(a capacity of 124 mAh g^(-1)after 10,000 cycles at 5 A g^(-1))is achieved.Theoretical calculations illustrate that sulfonate groups successfully induce charge redistribution on the carbon substrate,thereby strengthening the electronic interactions of the iodine species with the carbon substrate.The charge-enriched sulfonate groups can guide the uniform deposition of Zn^(2+)through a strong Coulombic effect with Zn^(2+).This work gives a new perspective on the integrated design of cathodes and anodes for rechargeable batteries.